I think i'm breaking the rules i apologize So my last guess is Tibetan Foothills! The secret is right next to the Snowmobile. There isn't snow or cold effect But the scenario is obviously snowy. The ice trap only falls down if you walk under them. Boulders as well but they are triggered 1 block before them. The hardest part is when Lara fights those snowmobile enemies imo.

__________________
"Too many people died for me to trust you. Including a good friend, Von Croy."

I think i'm breaking the rules i apologize So my last guess is Tibetan Foothills! The secret is right next to the Snowmobile. There isn't snow or cold effect But the scenario is obviously snowy. The ice trap only falls down if you walk under them. Boulders as well but they are triggered 1 block before them. The hardest part is when Lara fights those snowmobile enemies imo.

Don't worry about anyway Tibetan Foothills is correct!

1) How could I miss that secret?
I was actually referencing the jade dragon which is literally on a ledge right before you make a big jump on the snowmobile
2) How is Lara not injured by this?
Shooting through all the ice. You might expect Lara to get a couple of shards in her.
3) Oh CRAP!!!
The avalanche of snowballs/boulders near where you get the cabin key.
4) Stays still for hundreds of years until Lara walks under it.
The icicles!
5) Lara plainly does not get cold.
She doesn't get cold even when going in the water!